The present invention relates to a method for loading pellets into receptacles, such as, for example, loading catalyst into the vertical reactor tubes of a chemical reactor or a furnace.
Many chemical reactors are essentially a large shell and tube heat exchanger vessel, with the reaction occurring inside the tubes and a coolant circulating in the vessel outside the tubes. Furnace tubes are open gas fired from the outside along their vertical length while being mounted to a fixed manifold at the bottom and outlet pipes at the top. A chemical reactor vessel also can be a simple tank with a single volume of catalyst inside it, or it may be a single large tube. Some chemical reactions occur in steam reformer furnace and other tubes, which may be a part of a system with 10 to 500 or more such tubes. In any of these vessels and tubes, catalyst, typically in the form of pellets (and other types of pellets that are not catalyst), may be loaded into the tubes or vessels. The pellets are replaced periodically.
The tubes may be quite long, housed in a structure several stories tall, and the pellets may be transported up several stories to an elevation above the top of the tubes so they may then flow by gravity into the tubes. For instance, the tubes in many furnaces may be in excess of 45 feet (15 meters) long.
There is an effort in the catalyst industry to manufacture higher quality catalyst resulting in improved conversion efficiency. The conversion efficiency is impacted not only by the initial quality of the catalyst but also by the loading efficiency of the catalyst pellets. The pellets are carefully loaded into each reactor or furnace tube (there may be several thousand tubes in a single reactor) to try to uniformly fill each tube.
The catalyst pellets often are very frangible, that is, it is very fragile and brittle. The effort on behalf of the catalyst manufacturers to obtain a higher performance quality catalyst has resulted in even more delicate catalyst pellets with a lower crush strength. It is desirable to prevent degradation of the pellets during the handling and especially during the loading process. Dropping a pellet down a 45-foot-long reactor or furnace tube results in a high probability of breaking and degradation of the pellet, which is undesirable.
Pellets that are falling down a long tube achieve substantial velocity and kinetic energy, which must be dissipated when they land at the bottom of the tube or on top of other pellets. It can take time for pellets to dissipate their energy and come to rest. Some pellets may fracture simply by falling down the length of their respective tube. If the pellets are not given enough time to come to rest before other pellets are loaded on top of them, the packing density may be reduced, which is undesirable.
Many devices and methods have been used in the past to reduce the velocity and kinetic energy of the pellets as they are falling down a tube, including springs, “whiskers”, spiral ramps and other mechanical devices against which the pellets impact or slide along as the pellets flow downwardly through the receiving tube. Unfortunately, the repeated impacts of the pellets against these mechanical devices also tend to degrade the fragile pellets.
There exists a need for a device and a method for loading these pellets into reactor or furnace tubes (or other receptacles) that reduce the velocity and kinetic energy in order to reduce damage to the pellets and improve the packing density.